In recent years, processing of whole blood from a donor has come to routinely include separating the blood into therapeutic components. These components include red blood cells, platelets and plasma. Various techniques and apparatus have been developed to facilitate the collection of whole blood and the subsequent separation of therapeutic components therefrom.
One consideration in the processing of whole blood is the requirement that the processing take place under sterile conditions. A second consideration involves the requirement that unless the processing takes place within a single sealed system, the permitted storage duration and usable lifetime of the blood components is substantially shortened. Components processed within a sealed system can be stored for four to six weeks or longer before use. On the other hand, whole blood or components thereof must be used within 24 hours if the system seal is broken.
One very common step in the processing of whole blood into various therapeutic components includes centrifuging the blood so as to bring about the desired separation of those components.
To promote the desired ends of sterile processing within a single sealed system, a family of dual housing centrifuges has been developed. One example of this type of centrifuge is disclosed in U.S. Pat. No. Re. 29,738 to Adams entitled "Apparatus for Providing Energy Communication Between a Moving and a Stationary Terminal."
The Adams patent discloses a centrifuge having an outer rotatable housing and an inner rotatable housing. The inner housing is positioned within and rotatably supported by the outer housing.
The outer housing rotates at one rotational velocity, usually called one omega, and the inner rotatable housing rotates at twice the rotational velocity of the outer housing or two omega. There is thus a one omega difference in rotational speed of the two housings.
The centrifuge of the Adams patent is particularly advantageous in that no seals are needed between moving and non-moving parts. Further, the system of the Adams patent, provides for the processing of blood into components in a single sealed system wherein whole blood from a donor can be infused into the centrifuge while the two housings of the centrifuge are being rotated.
The system of the Adams patent uses a single motor coupled by gears and shafts to the two housings so as to provide the desired speed synchronization. This is an open loop system.
While the centrifuge of the Adams patent provides an apparatus wherein blood processing may take place in a single sealed sterile system, the mechanical apparatus of the Adams patent is subject to wear of the type normally experienced with gear driven systems. Hence, centrifuges in accordance with Adams disclosure must be built as precision mechanical systems. Since it is an open loop system, care must be exercised to insure that the two chambers do in fact continually operate at the desired speeds.
An alternate to the mechanical apparatus of the Adams patent is illustrated in U.S. Pat. No. 4,056,224 to Lolachi entitled "Flow System for Centrifugal Liquid Processing Apparatus." The system of the Lolachi patent includes a dual chamber centrifuge of the Adams type. The outer housing of the Lolachi centrifuge is rotated by a single electric motor which is coupled to the internal rotatable housing by belts and shafts.
The Lolachi mechanism, as was the case with the Adams mechanism, is an open loop, essentially mechanical, structure for driving the two rotatable housings. U.S. Pat. Nos. 3,986,442 and 4,113,173 illustrate alternate, open loop drive systems.
U.S. Pat. No. 4,108,353 to Brown entitled "Centrifugal Apparatus With Oppositely Positioned Rotational Support Means" discloses a centrifuge structure of the Adams type which includes two separate electrical motors. One electric motor is coupled by a belt to the outer housing and rotates the outer housing at a desired nominal rotational velocity. The second motor is carried within the rotating exterior housing and rotates the inner housing at the desired higher velocity, twice that of the exterior housing.
Tachometer feedback is provided from the second motor through a set of slip rings or brushes for the purpose of continuously controlling the speed of the second motor with respect to the first motor. The structure of the Brown patent thus provides for obtaining electrical signals corresponding to the velocity of the inner motor for the purpose of continually controlling the speed thereof by means of a closed loop control system.
U.S. Pat. No. 4,109,855 to Brown et al. entitled "Drive System For Centrifugal Processing Apparatus" discloses yet another drive system. The system of the Brown et al. patent has an outer shaft, affixed to the outer housing for rotating the outer housing at a selected velocity. An inner shaft, coaxial with the outer shaft, is coupled to the inner housing. The inner shaft rotates the inner housing at twice the rotational velocity as the outer housing. The mechanism of the Brown et al. patent is an open loop system.
A further alternate to the Adams structure is illustrated in U.S. Pat. No. 4,530,691 to Richard I. Brown entitled "Centrifuge With Movable Mandrel." The specification and figures of this Brown patent are hereby incorporated by reference herein. The centrifuge of this latter Brown patent also is of the Adams-type. However, this latter centrifuge has an exterior housing which is hinged for easy opening. When the hinged upper section is pivoted away from the bottom section, it carries the rotatable inner housing along with it.
The inner housing supports internally therein a spring biased mandrel which continually presses against a sealed, blood containing, container positioned within the inner housing. The system of this latter Brown patent also discloses the use of two separate electric motors to rotate the inner and outer housings. The motors are coupled to a control system.
Thus, while it is known from the prior art to use two independent motors in connection with a control system to rotate the dual housings of an Adams-type centrifuge, there are no known non-contact systems for acquiring or collecting velocity information from the inner rotating housing. Additionally, none of the prior art systems have provided control information concerning the direction of rotation of the inner housing.
Further, it has long been known from the manual centrifuge operations by which whole blood has been processed that when the blood is subjected to the centrifuge processing, the red blood cells become packed in one portion of the sealed container and are separated from the plasma. An optically discernible interface appears between the separated plasma and packed red blood cell components.
In view of the fact that the inner housing of the Adams-type centrifuge is usually positioned within the outer housing, it is not possible to easily and to visually determine the location of the interface between the plasma and the packed red blood cells. Hence, there continues to be a need to be able to dynamically detect the position of this interface while the two housings of the centrifuge are being rotated.